The automotive industry is in need of a battery technology that affords high voltage, high power, low cost, long life and recyclability for a growing number applications such as in hybrid electrical vehicles (HEV). Valve-regulated lead-acid (VRLA) battery technology may meet or exceed many of the requirements for low cost, sufficient power, and recyclability and very recently has been demonstrated to meet the life requirements in terms of high rate partial state of charge cycling. Despite these positive attributes, improvements in VRLA technology may be required to improve energy density, form, function, fitment and thermal management, particularly for use in hybrid electric vehicles.
One type of VRLA battery technology that may be used is spiral-wound cell technology. Spiral-wound VRLA cells are typically more compact than conventional lead-acid batteries and offer very high power and extended cycle life. Such cells typically include spaced-apart positive and negative plates having a grid-like construction.
The elongated grid structure for a spiral-wound VRLA battery is filled with the active materials to form either positive or negative plates. Sandwiched between the positive and negative plates is a thin porous absorptive glass matte (AGM) separator. The plates-separator assembly is wound into a compact rugged cylindrical form with the positive and negative plates and separator between the plates. The separator electrically isolates the plates from each other, and also functions as an effective wick or absorbent to retain the cell's electrolyte (an aqueous solution of sulfuric acid) between the plates and keep it evenly distributed in the working area of the cell. The thin, highly porous separator also keeps the ionic path between the positive and negative plates short and permits rapid diffusion of electrolyte. Thus the closely spaced construction of the plates and separator all contribute to the cell's ability to be discharged at high rates.
The typical spiral wound VRLA cell also generally includes a predetermined ratio of positive to negative active material that is sufficient to optimize battery life and performance while minimizing the formation of gases in the cell. A resealable vent is provided for the VRLA cell for releasing internal pressure in the cell should excess or undesirable gases be generated.
One disadvantage of conventional spiral-wound VRLA batteries made of multiple VRLA cells is the space requirements for obtaining batteries with the desired voltage. The VRLA batteries are comprised of cells that typically have a high aspect ratio of length (L) to diameter (D) wherein L>D. Such VRLA cells tend to be positioned side by side and then connected in series with small wires and electrical clips to attain the required battery or system voltages.
Larger spiral-wound VRLA single cells (>5 Ah) and multi-cell batteries are produced for UPS applications and are sold in custom cell sizes resembling a juice can or can of soup. Single cells are used in 3, 6, or larger groups and positioned and electrically connected side-by-side in a similar manner to the smaller cells. When produced as multi-cell mono-block batteries, these mono-block batteries tend to be 2, 3 or 4 cell packages with cells positioned side-by-side. The cell-to-cell connections in these mono-block batteries are made internally in an attempt to minimize the battery “foot-print,” i.e., the planar space requirement for the battery.
Spiral-wound VRLA technology has also been introduced to the automotive battery industry for starting, lighting, and ignition (SLI) applications. Such batteries resemble a “6-pack” of beer or soda and may have suitable cranking power, long life, and adequate performance in automotive or marine applications. As with the smaller spiral-wound VRLA batteries described above, the spiral-wound SLI batteries use high aspect ratio cells. Despite the fact that these batteries may be constructed in a custom six-cavity container shape with cast-on-terminal inter-cell connections, these batteries are not typically compact and may not readily interconnected with one another for high voltage HEV applications.
Despite the varied application and design, conventional spiral-wound VRLA cells all have the same common feature related to their shape, that is, all spiral-wound VRLA batteries have a high aspect ratio wherein L>D. Accordingly, the conventional VRLA batteries tend to function better if placed side-by-side rather than stacked on top of each other. Electrical terminals for the VRLA batteries tend to protrude from the top of the cells thereby further limiting the ability to stack the high aspect ratio cells. High aspect ratio batteries also have tall grids in the L direction that may result in higher resistivity and more voltage losses in applications that require high power such as HEV. Attempts have been made to improve the high rate performance of these cells by using multiple internal tabs; however such attempts have had only limited success. It has been difficult to assemble relatively high voltage batteries (˜200 v), such as those required for HEV applications, from conventional VRLA cells or modules due to the need for wiring and lengthy intercell connections. There is therefore a need for a VRLA cell design for high voltage applications that has the ability to take full advantage of the spiral-wound cell technology.
In view of the foregoing and other needs, an embodiment of the disclosure provides a valve regulated lead-acid (VRLA) battery having a plurality of stacked, interconnected spiral-wound cells. Each cell has a length (L) less than a diameter (D) and each cell has a non-conductive case containing spiral-wound positive and negative plates, a separator between the plates, an acidic electrolyte, and a positive post and a negative post disposed through the case for electrical connection to an adjacent cell in series.
Another embodiment of the disclosure provides a valve-regulated lead-acid (VRLA) energy storage cell for a battery. The energy storage cell has a non-conductive case, spiral wound positive and negative plates and separator between the plates disposed in the case. A liquid electrolyte for energy transfer is disposed between the plates. The positive and negative plates have multiple tabs. A positive strap and post are connected to the positive tabs and a negative strap and post are attached to the negative tabs. The positive and negative posts are disposed through the non-conductive cover of the case. Terminals are attached to the exposed post ends to serve as inter-cell connections. The energy storage cell has a length (L) that is less than a diameter (D).
An advantage of the foregoing VRLA cell and battery is that stacking the cells may be possible by the nature of the low aspect ratio (L<D) of the cells. Accordingly, multiple cells may be interconnected with less space than with conventional spiral wound VRLA cells.
A secondary advantage of the spiral-wound cell having a low aspect ratio, i.e., L<D, is that cells having shorter grids in the L direction and thus may exhibit improved cell performance due to lower electrical resistance from one end of the cell to the opposite end of the cell. Also, by having the diameter greater than the length of the cells, more tabs may be used across the diameter of the cell thereby further reducing cell resistance values for cell interconnection. Cells having a larger diameter than height may provide more stable stacking arrangements due to a larger area for stacking the cells end to end.
For relatively large diameter spiral-wound VRLA cells, cells having a toroidal or open core design may provide for more uniform cooling of the cells using a variety of cooling mediums such as air, water, and heat transfer fluids. By contrast, conventional SLI batteries are prismatic by design and thus offer very little possibility for uniform cell cooling.